Method of surface finishing paper or fiber board and product of same



May 10, 1932. CLAPP 1,857,497

METHOD OF SURFACE FINISHING PAPER .OR FIBER BOARD AND PRODUCT OF SAMEFiled Feb. 14. 19 27 Patented May 10, 1932 :umrs s'mrss PATENT OFFICEALBERT I1. CLAPP, 0F DANVERS, MASSACHUSETTS MErEon or SURFACE rm smnePAPER on FIBER Beam) A m rnonuc'r or SAME Application filed February 14,1927. Serial No.'168,224.

This invention relates to the surface finishing of paper, and moreparticularly relatively thick papers such as fiberboard, While in thecourse of manufacture on modern papermaking machines and has for itsobject the production of a product having a hig{h finish or glaze andadapted for use as trun board, suitcase-board, or for use in othercatained hot, the fuzz pacities where a highly finished product isdesired.

In accordance with the method of the present invention, a board isformed on one of the usual types of papermaking machines, passed overdriers, and then immediately before or during calendering, an aqueoussolution of a glaze-imparting sizing, such as sodium silicate solution,is applied on either or both faces of the board. Such sizing materialpenetrates rapidly into the surface portion 0 the board, but inasmuch asthe board immediately passes into the nip of the calender, there is aninsufficient time interval to produce a complete penetration of thesolution through the board, and accordingly a crushing or tearing of theboard while under heavy pressure in the nip of the rolls is prevented.As the surface-impregnated board passes through the rolls, which arepreferably mainon its surface is ironed down and pressed into thesilicate, which retains it in such condition and hardens or sets ondrying to impart a high finish or glaze to the board.

It is essential that the board being finished by my method be eitherunsized or filled with material having high aflinity for sodium silicatesolution. For instance if it be attempted so to finish a sized board, itis found that the calender rolls are gummed and the board tends to stickto and wind around the rolls, as a sized board so resists thepenetration of the silicate solution that a considerable portion of thesolution is retained on the rolls. When, on the other hand, the board'isunsized or filled with material having high affinity for silicatesolution, the solution penetrates rapidly into its surface portion, sothat but little remainson the rolls and accordingly practically nodifficulty is encountered dur- The applicability of the presentinvention may best be understood by reference to a specific example ofprocedure which is to be described in conjunction with the accompanyingdrawings, wherein Figure 1 represents in side elevation a portion of thedryers and a stack of calender rolls, certain of which rolls receive thesilicate solution from receptacles and apply it to the faces of theboard.

Figure 2 represents in plan view the calender stack.

Figure 3 is a section through the two upper calender rolls, on the line3-3 of Figure 2.

Figure 4 shows an enlarged section through a board surface-finished asherein described.

Referring to the drawings, the board S is passed from the dryer rolls 7of the machine f under a guide and tension roll 8 to the top of thecalender'stack and then successively between each of the pairs ofsuperposed rolls to the bottom of the stack, whereupon, if desired, itmay be slit and reeled. As shown, the sizing is applied to the side-s ofeach of the uppermost calender rolls 9, 9a, from re-' ceptacles 10. Thereceptacles are constructed and arranged similarly to the water boxes,so called, sometimes employed in water-finishing paper. Each receptacle,as illustrated, is provided with a bottom 10a and ends 105, whichconform accurately to the contour of the roll, so that a supply of thesizingmay v be maintained in the receptacle, which may be supported atits ends by brackets 11 secured to the framework 12. While rotating,each of the rolls '9, 9w picksup a film of the sizing and applies it tothe surface of the board with which it contacts, the thickness of thefilm being determined by the clearance between the roll and a doctor 13extending from end to end across the receptacle 10a near its top. Ofcourse, other methods of applying the sizing to the faces of the boardimmediately beforeor during calendering may be practised. For instance,the re v cepta'cles 10 maybe arranged to apply the sizing directly tothe faces of the board while on the calender rolls. Or suitable coatingor spraying devices may be used to apply the sizing to before it reachesthe calender rolls or While on the rolls. As the surface-sized boardpasses through the calender rolls, the fuzz or nap on its surfaces isironed down and pressed into the sizing, which retains it thus andhardens or sets upon drying to produce a finished and glazed surface a,as shown in Figure 4.

In preparing a strong board suitable for use in the manufacture oftrunks and suitcases, for example, the following procedure may be.adopted. Eighty parts of kraft and 20 parts of rag fiber are. chargedinto the beater engine together with suflicient water to ensurecirculation of the fiber. If desired,

other strong fiber, such as manila-or jute, may

be used in lieu of the kraft fiber. The fiber is beaten, say, for six toeight hours, so as to effect sufficient hydration of the fiber to feltproperly on the paper machine. The fiber is then diluted to the desiredconsistency and run off on a paper machine into board of the desiredthickness. It is preferable, howcveiythat the board or paper he ofgreater than 5-point thickness, since if of insufiicient thicknessitbecomes enetratedthroughout, rather than only surfiice-penetrated, andis likely to become crushed or torn between the calender rolls. Thefurnish from which the board is made may of course be varied, dependingupon the quality of product which it is desired to realize. Forinstance, if it is desired to produce a relatively inexpensive board, afurnish composed of, say, 75% ground-Wood or waste papers and 25%sulphite fiber and beaten for about one hour before running off on apaper machine, may be employed. Or, if it is desired to produce a whiteboard, the furnish may be composed of bleached sulphite or rag fiber,either alone or in admixture. In any ofthe furnishes hereinbefore given,20% to leather scrap may be used in lieu of cellulosie fiber. Theleather scrap, when thoroughly beaten out, say for five to six hours,may be advantageous, as it. enhances the felting power of the furnishand apparently increases the wet strength of the board, so that suchboard while wet on the machine need be'handled with less care. After theboard is felted, it is passed over the usual driers, and thence throughthe, calender rolls. In passing through the calender-s, sodium silicatesolutionis applied to its surfaces from the receptacles 10. The solutionis preferably about 20 Baum, as this produces adequate penetration intothe board, and the desired finish.

' If a very dilute or very concentrated solution were employed,difliculty would be encountered, as a dilute solution would not imart ofthe desired body and finish to the oard, Whereas a concentrated solutionwould not penetrate into the board with sutlicient rapidity so that thecalender rolls would like- 1y become gummed and the board tend to stickand wind up on the rolls. If desired, pigments such as ochre, lampblack,or the like may be added to the silicate solution to produce a coloringof the surface of the board. Preferably, also, the vcalenders' aremaintained hot, say at 160 to 180 F., as a better finish is produced.

#In lieu of silicate solution, aqueous solutions of otherglaze-imparting, water-soluble sizes, such as glue,'easein, or starchesconverted or made soluble by alkali, may be used at the properconsistency, but silicate solution has been found to impart the bestfinish and at the same time the necessary body to the board.

A board finished as herein described may be varnished or lacquered,or-sin1ilarly surfaced with a small amount of surfacing material, inconsequence of the elimination of fuzz or nap, and in consequence of thesurface rcsistivityof the board to penetration by va'rnishes or lacquerscontaining linseed oil or similar organlc soly ent as the liquidvehicle.

A singular advantage of the method of the present invention is that aglaze or finish equivalent or superior to the glaze or finish producedby calendering or supercalendering board formed of fiber and beaten for12 to 16 hours or longer, is economically produced, for the method iscarried out while the board is in the course of its manufacture andWithout the use of special machinery.

The method herein described cannot be practised in connection with themethod of tub-sizing paper, for if paper were tub-sized larly withmodern high-speed paper machincry. When paper is tub-sized, it iscustomary to dry the paper slowly, as by festooning it or passing itthrough a drying cham er, as it is of insuflicient strength to passrapidly over driers. If tub-sized paper were then calendered, the fuzzwould not be ironed out to produce a smooth, glazed surface such asherein described, and the hardened size would be crushed under thecalender rolls, It is thus necessary, in the practice of the presentinvention, to apply the sizing to the board immediately before passageinto the nip of the calender rolls, so that only surface impregnationoccurs, as the board is subjected to heavy pressure before-completepenetration has been effected. Preferably. the first. impregnationoccurs after passage through the first nip, as the tension on the paperis considerably reduced and there is hence less likelihood of tearingit.

Where sodium silicate or the other watersoluble sizes mentioned areemployed, the finish is not permanent ifthe board is subjected to wateror moisture, unless it is varnished, lacquered, or otherwisewaterproofed. In accordance with my process, however, I may produce afinish which is waterproof without the necessity of a waterproofcoating. This is accomplished by incorporating into the furnish a fillercapable of reacting with sonish then formed into board and such board istreated with sodium silicate, the sodium silicate reacts with suchfilling material to produce a cementitious material which upon dryingsets to a hard, waterproofing compound. In accordance with the processdescribed in my application, Serial No. 94,329, filed March 12, 1926,the board is saturated with silicate solution to produce a product whichis permeated'throughout with the waterproofing compound. In accordancewith the present process, however. the filled board is treated at thecalender rolls at its surface portions only, to produce a boardimpregnated at its surface portion only with the waterproofing compound.If the paper were saturated with silicate solution asdescribed in saidapplication, and then calendered, the board would be crushed or torn. Inproducing a water-resistant-board according to the present invention,the procedure may be as follows. To the furnish in the beater engine isadded 10% to 50% asbestos, or 5% to 20% lime, or a mixture of bothasbestos and lime in the desired proportion. The lime is preferablyhydrated finishing lime, so called, and is added before or during theinitial stages of beating, so as to be uniformly disseminated throughthe furnish. The asbestos fiber may be used in the form of therelatively short and'inexpensive fiber, such as is commonly used inmaking asbestos millboard. The asbestos fiber is preferably added afteror during the latter stages of beating, so that the length of fiber maybe preserved. If desired. the so-called-asbestos floats, or dust, whichis inexpensive. may be used in lieu of fiber.

The filled board is treated at the calender stack with sodium silicate,which reacts at its surface portions to produce a cementitious materialwhich functions to retain the fuzz ironed down, and upon drying sets toimpart .a glazed and water-resistant surface to the board.

The method of the present invention may be applied expediently insurface finishing multi-ply or liner boards in which the inner plies areformed of fiber sized as usual in the beater, and one or both outerplies are unsized or filled with asbestos, lime or the like, capable ofreacting to produce a glazeimparting waterproofing compound. Afterdrying, the multi-ply paper is treated at the calender stack with sodiumsilicate, which produces the desired finish.

I do not'herein claim the subject matter of my application, Serial No.89,502, filed February 19, 1926, wherein paper is surfacefinished orglazed while in the course of its manufacture, by treating it at' thecalender rolls with an aqueous dispersion of wax, and more particularlya sodiumsilicate dispersion of such waxes. In such case, the waxeseffect a surface sizing of the paper, as the sodium silicate solution isso dilute that it has practically no effect. In the present method, awater-soluble, glaze-imparting sizing is employed to effect the surfacefinishing and surface sizing of the paper.

Having thus described this invention, it is evident that it is capableof change and modification without departing from its spirit or scope asdefined by the appended claims. I

What I claim is: I I i 1. A process of treating unsized paper afterdrying while in the course of its manufacture, which comprises applyingan aqueous solution of a glaze-imparting slzmg to the surface of thepaper, and immediately calendering the same.

2. A process of treating unsized paper after drying while in the courseof its manufacture, which comprises applying an aqueous solution of aglaze-imparting sizing to the surface of the paper, and immediatelyhot-calendering the same.

3. A process of treating unsized paper after drying while in the courseof its manufacture, which comprises applying an aqueous sodium silicatesolution of about 20 Baum to the surface of the paper, and immediatelycalendering the same.

4. A process of treating dry, unsized paper above 5-points thickness,which comprises applying. an aqueous sodium silicate solution to thesurface of the paper, and immediately calendering the same.

5. A process of treating dry unsized paper above 5-points thickness,which comprises applying an aqueous sodium silicate solution containingpigments to thesurface of the paper, and immediately calendering thesame.

6. A process of treating dry paper filled with lime and asbestos, whichcomprises surface-treating the paper with an aqueous sodium silicatesolution and immediately calendering the same. 4

7 'A process of treating dry paper filled with a material capable ofreacting with silicate solution to form a glaze-imparting -waterproofingcompound, which comprises surface-treating the paper with an aqueoussodium silicate solution, and immediately calendering the same.

8. A calendered paper sized only at its surface portion with sodiumsilicate, said paper icate having been applied in the form of an aqueoussolution to the surface of the paper immediately before calendering.

9. A calendered paper surface-colored and -surface-sized with sodiumsilicate, said paper having the characteristics of said sodiumsilicatehaving been applied in the form of an aqueous solution to the surface ofthe paper immediately before calendering. p '10. A calendered paperfilled with material capable of, reacting with sodium silicate solutionto form a waterproofing, glaze imparting compound, and sized only at itssurface portion with the reaction product of so-. dium silicate and thematerial, said paper having the characteristics of said sodium silicatesolution having been applied to the surface of the. paper immediatelybefore calendering.

, 11. A calendered paper filled with lime and sized only at its surfaceportion with the reaction product of sodium silicate solution and lime,said paper having the characteristics of said sodium silicate solutionhaving been applied to the surface of the paper immediately beforecalendering.

12. A calendered paper filled with lime and asbestos, sized only at itssurface portion with the reaction product of sodium silicate solutionand with lime and asbestos, said paper having the characteristics ofsaid'sodium silicate solution having been applied to the surface of thepaper immediately before calendering.

In testimony whereof I have a'flixed my

